HistoMeter / HistoBlinkyMeter / EttR
DSLR Histograms on the LCD back
The histogram on the back of a Digital Single Lens Reflex camera (DSLR) is a representation of the tonal values in the image displayed there. It is extremely useful as a way to judge exposure, and has a feature called the "blinkies" which helps avoid overexposure. Using the histogram is part of "chimping". The histogram can guide you when using the EttR technique (Expose to the Right).
The histogram is shown on the back of the DSLR. You may have to read your manual to set your camera to display it, but all DSLRs do. On Canons, use the Info button while you have a picture displayed. One press adds some shot info, and a second press adds the histogram and more shot info. A third press gets back to the image with no info. There is an option in the menu of most Canon DSLRs to control whether it shows a B&W single histogram or three histograms for R, G, & B. I prefer the latter.
I call it a Histometer (my neologism of 2009) because it can be used as a light meter and often with greater effectiveness than the built-in camera meter.
The Histometer (see above) can also be termed a HistoBlinkyMeter (also my neologism, 2010) when you consider the Blinkies: blinking areas that indicate where the image has blown out highlights. In those areas it will be nearly impossible to recover good data. Some can be recovered if the image has been made in Raw mode (not JPEG mode).
The Joys of Chimping
Enjoy the use of the LCD on the back of the DSLR to look at the picture and the histograms. It was called "chimping" because of the oo-oo-oo sounds some people make when they get excited about the pictures. Don't be intimidated by film snobs who loftily state that they didn't have LCDs to chimp with, back in the day.
Expose to the Right (EttR)
The essence of this technique is to push the exposure up (more light) and then in processing bring the exposure down again. On the Histometer it will look as if the histogram has moved to the right.
The reason for doing this is to raise the shadow tones up out of the sensor noise as much as possible.